enhancerepo 0.3.1 cooking in build service: deltarpm support

The new feature is deltarpm metadata generation support and also some kind of smart deltarpm generation.

This means, enhancerepo can look which package has several versions in the repository, and generate delta rpms for N steps to the older versions. The default is one step, that is, only a delta rpm to the newest to the previous one. And then it can generate the metadata for you too (and add it to the index and such).

Be careful with running createrepo on top of a directory with deltarpms. createrepo will index them incorrectly as packages (So clean deltarpms, run createrepo, and then generate deltas with enhancerepo on top).